I think they're just orders. Isn't that the date they start to ship?
Since they are technically released on those days, you are right. There are no pre orders, just orders from that time.
Depends how much stock comes in by that date and how fast they sell. I can see some popular brands might become preorder within minutes.
Plus I cant see every model from every manufacturer being available right from day 1. EVGA are normally quite slow with their FTW and hydro copper cards and they tend to follow weeks after the more vanilla cards.